The report will be seized upon by critics of the health secretary, Jeremy Hunt, whose long-running dispute with junior doctors is based on claims that there needs to be more staff working on weekends to ensure patient safety.

MPs add that the DH has failed to assess the staffing implications of the Tories’ pledge for a seven-day NHS.

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Hunt wants to change the hours for which junior medics can claim premium rates of pay, turning 7am to 5pm on Saturday into a normal working day, but the report states: “The department has not adequately assessed the impact on the clinical workforce of implementing seven-day services and so does not know if there will be enough clinical staff with the right skills.”

The group of MPs are calling for an urgent review of NHS clinical staffing in England.

Meg Hillier, the chair of the committee, said there were serious flaws in the government’s approach to staffing the NHS.

“This poor workforce planning means patients face the possibility of longer waiting times and a greater cost to the public purse,” she said. “At the same time, taxpayers are being asked to accept uncosted plans for a seven-day NHS – plans which therefore present a further serious risk to public money.

“It beggars belief that such a major policy should be advanced with so flimsy a notion of how it will be funded. If the government hopes to reassure the public it has credible plans for staffing and service delivery, we urge it to demonstrate leadership.”

MPs point out in the report that there was a shortfall of about 5.9% of clinical staff working in the NHS in 2014, equating to a gap of about 50,000 staff. They warn that this shortfall inhibits the health service in providing an efficient and effective service.

In recent years, NHS trusts have been forced to reduce staff to meet efficiency targets, the report suggests, pointing out that the NHS meets the staffing need by using more costly agency staff, “thereby increasing the financial pressure on the NHS”.

The report criticises the DH for “ineffective leadership and support, giving trusts conflicting messages about how to balance safe staffing with the need to make efficiency savings”.

Dr Mark Porter, chair of council at the British Medical Association, said: “This report further underlines the government’s failure to consider how it will staff and fund additional services when the NHS is struggling to provide existing services.

“Despite what ministers claim, NHS funding has not kept up with rising patient demand and the increased cost of delivering care. This situation is only set to get worse, not least because the government’s handling of the junior doctor contract, which has alienated a generation of doctors. This is disastrous for the delivery of patient care in the long term.”

The DH said the report did not take into account an increase in the number of staff or plans to increase capacity to deliver a seven-day NHS.

“By 2020, we expect to have 11,420 more doctors working in the NHS, coupled with 10,000 nursing, midwife and allied health professional training places through our reforms. By March next year, we will provide a quarter of the population with 7-day care,” it said.